PROTEIN-KINASE-C INHIBITS ADENYLYL-CYCLASE TYPE-VI ACTIVITY DURING DESENSITIZATION OF THE A2A-ADENOSINE RECEPTOR-MEDIATED CAMP RESPONSE

We have previously reported that phosphorylation of adenylyl cyclase t ype VI (AC6) may result in the suppression of adenylyl cyclase activit y during desensitization of the A2a-adenosine receptor-mediated cAMP r esponse (A2a desensitization) in rat pheochromocytoma PC12 cells. In t he present study, we demonstrate that protein kinase C (PRC) is respon sible for the phosphorylation and inhibition of AC6 during A2a desensi tization. Inhibition of PKC by several independent methods markedly bl ocked the suppression of AC6 during A2a desensitization. Purified PKC from rat brain directly phosphorylated and inhibited recombinant AC6 e xpressed in Sf21 cells. Substantially lower AC6 activities were also o bserved in PC12 cells overexpressing PKC delta or PKC epsilon. Stimula tion of A2a-R in PC12 cells under the same conditions as those require d for A2a desensitization resulted in an increase in Ca2+-independent PKC activity. Most importantly, exogenous PKC did not further suppress AC6 activity in A2a-desensitized membranes. In vitro PKC phosphorylat ion of AC6 isolated from A2a-desensitized cells was also profoundly lo wer than that from control cells, suggesting a specific role for PKC i n regulating AC6 during A2a desensitization in PC12 cells. Taken toget her, our data demonstrate that a calcium-independent, novel PKC inhibi ts AC6 activity during A2a desensitization in PC12 cells. Independent regulation of AC6 by calcium-independent PKC and by Ca2+ provides an e xquisite mechanism for integrating signaling pathways to fine-tune cAM P synthesis.